[Sruti Visweswaran]

I’ve been working with mixed formats on an edit for while. Most of the footage was HD and just one section was SD. As a workflow, we were editing on an HD timeline since most of the footage was HD.

In your case, bringing HD to an SD anamorphic timeline and taking it back to a 1920×1080 timeline for export will have a bearing on the HD material only if it has been either rendered or exported and then brought back in to the timeline. The logic behind it is that with every generation of conversion and export, there is a small amount of loss in image quality. This loss is cumulative with every subsequent conversion as you are, at every stage, making a physical alteration t the original footage. These may not be noticeable in most well-lit shots but you will see the difference if you have a lot of detail in your highlights and your blacks.

When you bring your HD material onto an HD timeline from the SD timeline, make sure you remove all motion attributes like scale, distort and centre.

You should be fine if you take your final HD output using compressor.

I hope this helps!